Sensor

ABSTRACT

An energy-autonomous sensor for detection of physical environmental parameters, having at least one sensor element, one storage element and one control circuit, with a timer circuit which is activated on reaching a predetermined electrical voltage on the storage element, activates the sensor and the control circuit at predetermined time intervals, and deactivates them after a predetermined operating time, such that this results in a time duration of sensor operation and a sensor operation pause.

RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 11/183,092,filed Jul. 15, 2005, now U.S. Pat. No. 7,389,674, which is acontinuation of International Application No. PCT/DE2004/000034, filedon Jan. 14, 2004, which claims priority from German Patent ApplicationNo. 103 01 678.3, filed on Jan. 17, 2003, the contents of all of whichare hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to a sensor for detection of physicalenvironmental parameters, having at least one sensor element, onestorage element and one control circuit.

BACKGROUND OF THE INVENTION

Sensors, as well as energy-autonomous sensors, for detection ofmeasurement values and other physical variables are known, for example,from EP 0918212 A1. This document discloses sensors, which detectmeasurement values and pass on the measurement values to an evaluationdevice which is, in particular, central and operates on a computer-aidedbasis. The word “central” means that a plurality of sensors communicatewith the same evaluation device. In order in this case to avoid complex,costly and visually highly disadvantageous wiring and an operating timewhich is limited in the case of battery and rechargeable batteryoperation and the need, associated with this, for the replacement andcharging of the electrical power source at regular intervals, sensors,in particular temperature sensors, are proposed there, which detectmeasurement values and pass on the measurement values to an evaluationdevice which is, in particular, central and operates on a computer-aidedbasis, with the measurement values being passed on by means of radiotransmission from a sensor device, which is connected to the sensor andhas an antenna, to an evaluation device, and the transmission devicebeing supplied with electrical power from an electrical power generatorwhich converts the energy in the surrounding area.

In order to detect physical variables whose energy cannot sufficientlybe converted to electrical energy, so that the sensor can thus beoperated, such as moisture or humidity, it is necessary to convert otherenergy forms which are available at the location of a sensor toelectrical energy, or to provide energy stores in situ, for examplebatteries or rechargeable batteries. In the case, for example, of themeasurement of the moisture or humidity in the immediate vicinity, closeto the ground, of a plant, it is not possible to assume that there iseither sufficient thermal or kinematic energy for conversion toelectrical energy, so that, for example, the light or solar energy mustbe used for conversion to electrical energy at this point.

The document U.S. Pat. No. 5,601,236 A discloses an apparatus formoistening and growth promotion of plants, in which this apparatus alsohas a moisture or humidity sensor, an energy store, a solar module and acontrol circuit, and an external timer starts a controller program whichdetects the amount of charge remaining in the system and/or in theenergy store and determines the charge currently being supplied from thesolar cells, with this being used to determine whether sufficient energycapacities are available in order to operate the various modules in theoverall system. If sufficient energy is not available, the externaltimer is reset by a further period and the controller program causes allof the modules to return to a sleep mode until the time interval haselapsed once again and the check commences from the start.

The document GB 2320572 A discloses a plant moisture detector with asolar cell which operates an oscillator, which in turn detects thecapacitive and/or resistive impedance of the ground via two separatelyrunning lines. This value is a measure of the moisture in the ground.

The document “Low Power System for Wireless Microsensors” Proceedings ofInternational Symosium on Low Power Electronics and Design, XX, XX, 12Aug. 1996, pages 17-21, XP001013406 by Bult, K. et al. discloses in ageneral form a network of wire-free sensors for applications in thetransport field, production field, biomedical and environmental fieldand for safety and security systems. Numerous microsensors with a verylow power consumption are connected to a central evaluation station viaa radio link.

The document “Power Aware Wireless Microsensor Systems” ESSCIRC,September 2002, XP002288893 Florence, Italy published by Chandrakasan,A. et al. discloses a low power transmitter with a short starting time,which reduces the amount of energy required per transmitted bit of aradio link.

A system for measurement of moisture or humidity with radio transmissionof the measurement values to a central evaluation device and with asolar energy power supply to the sensors is proposed in U.S. Pat. No.4,396,149. In this case, a continuous measurement is carried out bymeans of the sensor, and energy is supplied continuously by means of aphotovoltaic element. Photovoltaic elements of adequate size must beprovided in order to provide an adequate power supply for the sensorelement with radio transmission and for continuous measurement. This isnot desirable and advantageous for all applications. If a sensor elementis intended to provide its service in such a way that it is small,inconspicuous and reliable, in particular even at times when the lightis poor, for example, at night, then neither the apparatus according toEP 0918212 A1 nor the apparatus according to U.S. Pat. No. 4,396,149 issuitable.

SUMMARY OF THE INVENTION

One object of the invention is to detect physical variables with anenergy-autonomous sensor which is able to detect physical variablesreliably and regularly even when only a weak supply, or at times nosupply, of primary energy such as light which can be converted toelectrical energy is available at the measurement location.

This and other objects are attained in accordance with one aspect of theinvention directed to an energy-autonomous sensor for detection ofphysical environmental parameters, comprising one storage element forstorage of electrical energy, one sensor element for detection ofphysical environmental parameters, one control circuit for coding of thedetected physical environmental parameters, a photovoltaic element whichis connected to the storage element in order to supply power to thesensor, and a timer circuit. The timer circuit which is activated upon apredetermined electrical voltage on the storage element being reached,activates the sensor element and the control circuit at apredeterminable time interval, and deactivates them after apredeterminable operating time, such that this results in a timeduration of sensor operation and time duration of a sensor operationpause.

It is advantageous, particularly with regard to saving the availableenergy, to design the time duration of sensor operation to beconsiderably shorter than the time duration of the sensor operationpause.

One embodiment of the invention is a sensor which passes on informationto other devices, for example, to a watering controller that is linkedto a main electrical power system, or to a bus system. The energy foroperation of the sensor and of the associated radio circuit is producedfrom the environmental light, so that no battery is required foroperation. Both wire-based and radio-based systems can be used fortransmission of the information. The use of radio-based informationtransmission from the sensor according to the invention to anotherdevice includes the advantage that, for example, no transmission linesneed be arranged between the other device and the sensors.

In another embodiment of the invention, a photovoltaic element producesan electrical voltage when light is incident, in order to supply powerto the sensor. This photovoltaic element is designed such that a voltageof about 2 volts is emitted even when the illumination intensities arelow. Since the power that is produced is in general not sufficient forcontinuous operation of the sensor, a storage element, preferably atleast one of a capacitor and an electrochemical energy store, is firstof all charged with electrical energy.

When the electrical voltage on the storage element reaches apredetermined level, a timer circuit is activated which activates anddeactivates the entire sensor at predetermined intervals. In oneembodiment of the invention, the time intervals for activation anddeactivation of the sensor are variable, and can be redefined by thecontrol circuit on each activation. For this purpose, in particular, thestate of, charge of the storage element, optionally as well as theillumination intensity, is checked via the solar cell. Both or else onlyone of the two parameters are or is included in the redefinition of thetime intervals. This allows the sensor to be operated for as long aspossible even in darkness phases, that is to say in phases in which itis not feasible to supply energy from the environmental energy.

Furthermore, the photovoltaic element can additionally be used tomeasure the illumination intensity on each activation of the sensor. Theillumination intensity can be transmitted together with an ID number ofthe sensor, the value of the measurement sensor, for example, themoisture or humidity measurement sensor.

In another embodiment of the invention, a radio-frequency transmitterand an antenna, which is connected to it emit the coded information andtransmit it to other devices. In order to improve the transmissionreliability, the radio signal for this transmission is advantageouslydesigned to be redundant, that is to say it is transmitted using a widebandwidth and/or in a time sequence.

The radio signal can be received, and is evaluated, by all of theassociated radio-frequency receivers which are located in the vicinity.After the evaluation process, addressable receiver systems which areconnected thereto react and in turn result in an action, such as openingof a watering device and/or control of an optical or acoustic signalingdevice, and/or feeding of the measurement data to a system for furtherstorage and/or processing of the measurement data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary embodiment of the present invention,illustrated schematically;

FIG. 2 shows a refinement of the sensor 1 with a photovoltaic element 2;

FIG. 3 shows an additional refinement of the sensor illustrated in FIG.2 with a radio-frequency transmitter 6;

FIG. 4 shows a receiving device 8, illustrated schematically; and

FIG. 5 shows an exemplary embodiment of the sensor 1 as a moisture orhumidity sensor.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sensor 1, illustrated schematically, with an electricalcharge that is supplied to the sensor 1 being stored in a storageelement 3. This storage element 3 is preferably formed from a low-losscapacitor 3.2 with a high capacitance. The storage element 3advantageously contains a storage circuit 3.1 which, in a simple case,by way of example, comprises a semiconductor diode or a rectifiercircuit. This is illustrated symbolically in FIG. 1 by the symbol of adiode. The storage circuit 3.1 in this case prevents charges fromflowing back from the storage element 3 to a power supply device that isconnected, but is not illustrated in FIG. 1. A further optional functionof the storage circuit 3.1 is impedance matching between a power supplydevice and the storage element 3.

In an embodiment that is illustrated in FIG. 2, a photovoltaic element 2is connected as the power supply device. The photovoltaic element 2 ispreferably chosen to be sufficiently small to be able to achieve a veryhigh degree of flexibility in terms of the choice of the point of use.Direct operation of the sensor 1 with the photovoltaic element 2 is thusimpossible. The energy that is produced by the photovoltaic element 2 iscollected in a storage device for operation of the sensor 1. In theexemplary embodiment illustrated in FIG. 2, a storage element 3 issupplied and filled with electrical charge by the light that is incidenton the photovoltaic element 2.

The size of the low-loss capacitor 3.2 for the storage device 3 isselected in conjunction with the photovoltaic element or any other powersupply device such that even extreme darkness phases, such as thosewhich may occur by way of example at night, in particular during thewinter months, can be reliably reconciled, that is to say the storageelement 3 is supplied and can also store sufficient energy via thephotovoltaic element 2 to allow timer operation and sensor operation totake place in time intervals, even during the darkness phase.

The timer circuit 12 which is illustrated in FIG. 1 is designed usingULP (ultra low power) technology, so that it can operate with extremelylittle energy consumption. For this purpose, the timer circuit 12 isdesigned using analogue or digital technology. The timer circuit 12 isthe only component of the sensor 1 that is operated continuously. Thetimer circuit 12 activates the control circuit 5, with the sensorelements 4 connected to it, at regular, predetermined time intervals,and deactivates them after a predetermined operating time. In this case,the time duration of an operating phase of the sensor 1 is considerablyshorter than the time duration of a pause in operation of the sensor 1.

In one advantageous embodiment, which is illustrated in FIG. 2, thetimer circuit 12 activates the control circuit 5 as well as the sensorelement 4 as a function of the state of charge of the storage element 3;and, optionally or additionally, also as a function of the illuminationintensity at the photovoltaic element 2. Any sensor element whichconverts a physical variable to an electrical signal, and has thecapability to pass this on to the control circuit 5, is suitable for useas the sensor element 4 for detection of the physical variable.

In one exemplary embodiment, which is illustrated in FIG. 5, animpedance measurement of the ground is preferably provided, by means ofa number of electrodes, but at least two electrodes, for measurement ofthe moisture or humidity, in particular for measurement of the groundmoisture.

FIG. 3 shows a schematic illustration of one advantageous embodiment forradio-based transmission of the information that is detected by thesensor 1. In this case, the timer circuit 12 activates the controlcircuit 5 as well as the sensor element 4 and a radio-frequencytransmitter 6 as a function of the state of charge of the storageelement 3; and, optionally or additionally, also as a function of theillumination intensity at the photovoltaic element 2. Theradio-frequency transmitter 6 is preferably equipped with aradio-frequency oscillator 14, which has a very fast transient response.In this case, a surface acoustic wave resonator may be used as thefrequency-determining component. The radio-frequency transmittermodulates the information that is detected by the sensor 1 onto aradio-frequency signal or radio message.

In order to keep the energy consumption of the radio-frequencytransmitter 6 low, it is designed to draw little current and operateswith a wide bandwidth, in order to keep the transmission duration short.Owing to the wide bandwidth, this results in a short transmission timeand thus in extended, low energy consumption. The radio-frequency signalor radio message is transmitted via the antenna 7 that is connected tothe radio-frequency transmitter 6.

FIG. 4 shows a receiving device 8 for reception of the information thatis transmitted from the radio-frequency transmitter, with this receivingdevice 8 having at least one antenna 9 for reception of theradio-frequency signal or radio message, and a radio-frequency receiver10 which is connected to this antenna 9. This radio-frequency receiver10 receives the signals transmitted from the sensor 1, demodulates themand passes them to an evaluation device 11. The evaluation device 11 hasconnections 15 to which further systems or actuators are connected.These are, for example, watering systems, signaling systems or othersystems.

Error-tolerant transmission methods, such as parity check, forward errorcorrection or block-oriented redundancy methods, are preferably used fordata transmission. It is also possible to scramble the transmitted datausing suitable electronic keys. The data is transmitted in a very shorttime and at predetermined time intervals. In this case, the transmissiontime is considerably shorter than the time in which no transmissiontakes place. This considerably reduces the collision probability of twosensors 1 transmitting at the same time.

Not only the measured physical parameter, but also further informationthat is produced at the sensor 1, may be used as the data contents fortransmission, such as an ID number of the sensor 1 the temperature thatoccurs at the sensor 1, the illumination intensity at the sensor 1 atthe time of transmission, the water level adjacent to the sensor 1, andmany other possibilities.

FIG. 5 shows one embodiment of a sensor 1 in the form of a rod with aphotovoltaic element 2, a storage element 3, a control circuit 5 and aradio-frequency transmitter 6, whose measurement electrodes 13 areintroduced into the ground or a′ water reservoir in order to measure theground moisture via an impedance measurement. Modulated direct currentor alternating current is preferably used for impedance measurement,with at least one frequency, but preferably two or more frequencies,being used when using alternating current. This type of impedancemeasurement makes it possible to determine the ground moisture withconsiderably better independence of the ground characteristics than apure direct-current measurement.

The scope of protection of the invention is not limited to the examplesgiven hereinabove. The invention is embodied in each novelcharacteristic and each combination of characteristics, which includesevery combination of any features which are stated in the claims, evenif this combination of features is not explicitly stated in the claims.

1. An energy-autonomous sensor for detection of physical environmentalparameters, comprising: one sensor element for detection of physicalenvironmental parameters; a control circuit for coding of the detectedphysical environmental parameters, a radio-frequency transmitter fortransmitting the coded detected physical environmental parameterstogether with an ID number of the sensor; a storage element for storageof electrical energy; an electrical power generator adapted to convertenergy in the surrounding area into electrical energy and wherein theelectrical power generator is coupled to the storage element in order tosupply power to the sensor; and a timer circuit which is activated upona predetermined electrical voltage on the storage element being reached,activates the sensor element and the control circuit at a predeterminedtime interval, and deactivates them after a predetermined operatingtime, such that this results in a time duration of sensor operation andtime duration of sensor operation pause.
 2. The sensor of claim 1,wherein the electrical power generator is a photovoltaic element and isconfigured to be smaller than is required for direct operation of thesensor with the control circuit.
 3. The sensor of claim 1, wherein theradio-frequency transmitter is configured to transmit by error-toleranttransmission methods and/or to scramble the coded detected physicalenvironmental parameters together with an ID number prior totransmission.
 4. The sensor of claim 1, wherein the time duration ofsensor operation is shorter than the time duration of the sensoroperation pause.
 5. The sensor of claim 1, wherein on each activation ofthe control circuit, the time interval for activation of the controlcircuit is a function of the state of charge of the storage element. 6.The sensor of claim 1, wherein the time interval for activation of thecontrol circuit is a function of the illumination intensity at thephotovoltaic element at the activation time.
 7. The sensor of claim 1,wherein the radio-frequency transmitter produces at least one of aradio-frequency signal or radio message.
 8. The sensor of claim 1,wherein the storage element is a capacitor and/or an electrochemicalenergy store.
 9. The sensor of claim 1, wherein the sensor elementdetects moisture or humidity as the physical environmental parameter.10. The sensor of claim 1, further comprising at least two electrodesfor performing a moisture or humidity measurement via an impedancemeasurement.
 11. A system comprising: an energy-autonomous sensor fordetection of physical environmental parameters comprising: one sensorelement for detection of physical environmental parameters; a controlcircuit for coding of the detected physical environmental parameters; aradio-frequency transmitter for transmitting the coded detected physicalenvironmental parameters together with an ID number of the sensor; astorage element for storage of electrical energy; an electrical powergenerator adapted to convert energy in the surrounding area intoelectrical energy and wherein the electrical power generator isconnected to the storage element in order to supply power to the sensor;and a timer circuit which is activated upon a predetermined electricalvoltage on the storage element being reached, activates the sensorelement and the control circuit at a predetermined time interval, anddeactivates them after a predetermined operating time, such that thisresults in a time duration of sensor operation and time duration ofsensor operation pause; and at least one radio-frequency receiver forreceiving and evaluating the coded detected physical environmentalparameters together with the ID number of the sensor, wherein theradio-frequency receiver is connected with addressable receiver systemsthat react and in turn result in an action.